1. Field of the Invention
The present invention relates to an electrical tool, in particular a circular saw, including a housing, a motor-driven hollow spindle for supporting a working tool and located in the housing, and a quick-action device for clamping the working tool with respect to the hollow spindle and having a clamping spindle arranged in the hollow spindle with a possibility of an axial displacement relative thereto, an elastic member for biasing the clamping spindle into its clamping position in which the working tool is clamped between a clamping flange, which is provided on a working tool-side end of the clamping spindle, and the hollow spindle, and actuation means for displacing the clamping spindle against a biasing force of the elastic member into its exchange position in which the working tool is released.
2. Description of the Prior Art
As discussed above, the electrical tools of the type discussed above have a quick-action clamping device that provides for an easy exchange of the working tool, e.g., a circular saw blade, without danger of loosing the working tool. The working tool is releasably secured with a clamping flange, which is provided on the clamping spindle, as a result of the movement of the clamping spindle relative to the hollow spindle. Preferably, the quick-action clamping device includes means for formlockingly securing the working tool in the quick-action clamping device.
An electrical tool of the type described above, is disclosed, e.g., in German Patent No. 4,336,620. the disclosed tool includes a motor located in the tool housing for driving the hollow spindle, and a quick-action clamping device for receiving the working tool. The quick-action clamping device includes a clamping spindle displaceably supported in the hollow spindle coaxially therewith. The clamping spindle is axially preloaded by an elastic member. The quick-action clamping device is actuated between its clamping and release positions by a clamping lever provided at the end of the clamping spindle remote from the working tool-side end of the clamping spindle. In the clamping position of the quick-action clamping device, the working tool is clamped between the hollow spindle and the clamping flange. At the end of the clamping lever, at which the lever is supported on a pivot axis, there is provided an eccentric connected with the clamping spindle by a bolt. Upon pivoting the clamping lever into the exchange position, the eccentric displaces the clamping spindle against the biasing force of the elastic member and, as a result of frictional forces acting between the bolt and the eccentric, displaces the clamping spindle axially in a direction toward the working tool.
An advantage of the known quick-action clamping device consists in that the working tool can be exchanged without using any auxiliary tool, e.g., a spanner. For changing the working tool, a user moves the clamping lever into an exchange position and screws the clamping flange off the clamping spindle, which permits to take off the working tool and/or place a new tool in the quick-action clamping device.
A drawback of the know quick-action clamping tool consists in that in view of the manufacturing tolerances during the manufacture of the electrical tool, the quick-action clamping device should be readjusted during the final assembly.
Further, e.g., after a lasting use for a significant period of time, different expansions of elements of the clamping device, as a result of heating, adversely affect the functioning of the device. The different heat expansions of the device elements adversely affect the device behavior. In separate cases, even blocking of the quick-action clamping device is possible.
Accordingly, an object of the present invention is to provide a quick-action clamping device that would not be sensitive to manufacturing tolerances of the electrical tool in which the clamping device is used.
Another object of the present invention is to provide a quick-action clamping device that would reliably function even with a strong heating of the electrical tool.